1. Field of the Invention
The present invention relates generally to a valve timing control apparatus for controlling valve open/close timing (hereinafter referred to simply as the valve timing) at which an intake valve or an exhaust valve of an internal combustion engine is opened and/or closed in dependence on operating state or condition of the engine.
2. Description of Related Art
In the technical field of the internal combustion engine, there have heretofore been proposed various apparatuses which make it possible to controllably change the valve timing for the intake valve or the exhaust valve of the internal combustion engine (hereinafter also referred to simply as the engine) in dependence on the operation states thereof. For having better understanding of the invention, background techniques will first be described in some detail by reference to FIG. 18 of the accompanying drawings which shows generally and schematically a structure of an internal combustion engine equipped with a conventional valve control apparatus.
Referring to FIG. 18, reference numeral 1101 denotes generally an internal combustion engine which includes an intake pipe 1104 equipped with an air cleaner 1102 for purifying the air sucked into the engine 1101, an air-flow sensor 1103 for measuring intake air quantity (flow rate of the intake air), a throttle valve 1105 for adjusting or regulating the intake air quantity to thereby control the output torque of the engine 1101 and a fuel injector 1106 for injecting an amount of fuel compatible with the intake air quantity.
Further, the internal combustion engine 1101 is provided with a spark plug 1111 for generating sparks for firing air-fuel mixture charged in a combustion chamber of the engine 1101, an ignition coil 1110 for supplying a high-voltage energy to the spark plug 1111, an exhaust pipe 1107 for discharging an exhaust gas resulting from combustion of the air-fuel mixture, an O2-sensor 1108 for detecting a residual amount of oxygen contained in the exhaust gas, and a three way catalytic converter 1109 capable of purifying concurrently harmful gas components contained in the exhaust gas such as THC, CO and NOx.
A sensor plate 1116 having a tooth or projection (not shown) formed at a predetermined position is mounted on a crank shaft for corotation therewith for detecting the crank angle (angular position of the crank shaft) in cooperation with a crank angle sensor 1115 which is so designed as to generate a signal upon every passing-by of the projection (not shown) of the sensor plate 1116.
Further provided are a cam phase actuator 1113 for changing a relative angle of a cam shaft relative to the crank shaft and a cam angle sensor 1112 for generating a pulse signal upon passing-by of a projection of a cam angle detecting sensor plate (not shown) to thereby detect the cam angle in a similar manner as the crank angle sensor 14 described above.
Provided in association with the cam phase actuator 1113 are an oil control valve (hydraulic pressure regulating means) 1114 for regulating the hydraulic pressure applied to the cam phase actuator 1113 to thereby control the relative angle (cam phase) of the cam shaft relative to the crank shaft and an ECU (electronic control unit serving as arithmetic means as well) 1117 which is in charge of controlling the cam phase in addition to the control of operation of the internal combustion engine 1101 on the whole.
Further provided are an oil pump 1118 for generating a hydraulic pressure to drive the cam phase actuator 1113 while feeding a lubricating oil under pressure to mechanical constituent parts of the internal combustion engine 1101 and a hydraulic pressure sensor 1119 for detecting the hydraulic pressure of the lubricating oil fed under pressure to the oil control valve 1114 from the oil pump 1118.
Additionally, there are provided an oil temperature sensor 1120 for detecting temperature of the oil fed under pressure from the oil pump 1118 to the oil control valve 1114 and a water temperature sensor 1122 for detecting temperature of cooling water 1121 employed for cooling the engine 1101.
As a typical one of the hitherto known valve timing control apparatus (cam phase actuator) 1113 for the internal combustion engine 1101, there can be mentioned the one shown in FIGS. 19 to 23 of the accompanying drawings, in which FIG. 19 is a view showing an internal structure of a conventional vane-type valve timing control apparatus, and FIG. 20 is a vertical sectional view of the same taken along a line Axe2x80x94A shown in FIG. 19.
Further, FIG. 21 is an enlarged perspective view showing a major portion of a lock/unlock mechanism of the conventional vane-type valve timing control apparatus and FIGS. 22 and 23 are vertical sectional views showing the lock/unlock mechanism, respectively.
Next, referring to FIGS. 19 to 23, description will be directed to the conventional valve timing control apparatus 1113.
Referring to the figures, the cam phase actuator (valve timing control apparatus) 1113 includes a first rotor assembly 1 (FIG. 20) which is operatively coupled to the crank shaft (not shown) serving as the output shaft of the engine so that the first rotor assembly 1 rotates in synchronism with the crank shaft.
The first rotor assembly 1 is constituted by a sprocket 2 adapted to rotate together with the crank shaft, a case 3 having a plurality of projecting shoes 3a which project radially inwardly from the inner peripheral portion of the case 3 to thereby define a corresponding number of hydraulic chambers (FIG. 19), and a cover 4 (FIG. 20) for fluid-tightly closing the hydraulic chambers constituted by the projecting shoes 3a of the case 3, wherein the sprocket 2, the case 3 and the cover 4 are secured together by means of clamping members 5 such as bolts or the like (FIGS. 19, 20) in an integral structure.
Disposed within the case 3 rotatably relative to the first rotor assembly 1 is a rotor (second rotor) 6 (FIG. 19) which is integrally secured to the cam shaft 7 by means of a clamping member 8 such as a bolt or the like (FIG. 20). The cam shaft 7 constitutes a part of the mechanism for opening/closing the intake valve or the exhaust valve. The second rotor 6 includes a plurality of vanes 6a each of which serves to partition each of the hydraulic chambers defined by the projecting shoes 3a, respectively, of the case 3 into a valve timing advancing hydraulic chamber 9 and a valve timing retarding hydraulic chamber 10 (FIG. 19).
Further formed internally of the cam shaft 7 are first oil passages (hydraulic chamber feed passages) 11 through which hydraulic pressure is fed/discharged to/from the valve timing advancing hydraulic chambers 9, respectively, and second oil passages (pressure chamber feed passages) 12 through which the hydraulic pressure is fed/discharged to/from the valve timing retarding hydraulic chambers 10, respectively.
Disposed at a tip end portion of each of the projecting shoes 3a of the case 3 and a tip end portion of each of the vanes 6a of the second rotor 6, respectively, are oil sealing means 13 for preventing occurrence of oil leakage between the valve timing advancing hydraulic chamber 9 and the valve timing retarding hydraulic chamber 10 (FIG. 19).
Formed in one of the vanes 6a of the second rotor 6 is a receiving hole 14 for receiving therein a lock pin. More specifically, a lock pin 15 (which may also be referred to as locking member or locking mechanism) which is implemented as a straight pin of a substantially cylindrical shape is disposed within the receiving hole 14 for the purpose of restricting relative rotation between the first rotor assembly 1 and the second rotor 6 (FIG. 20).
In the engine starting phase or state in which no hydraulic pressure is effective internally of the cam phase actuator, the lock pin 15 serves to prevent the second rotor 6 from vibrating in the rotating direction under a reaction force of a cam (not shown) integrally secured to the cam shaft 7 to thereby suppress knocking noise (abnormal noise) which will otherwise be generated through repetitive impacts of the second rotor 6 on the first rotor assembly 1.
To this end, the lock pin 15 is constantly resiliently urged toward the first rotor assembly 1 under the influence of urging means (locking means) 16 such as a coil spring disposed between the rear wall of the receiving hole 14 and the lock pin 15 so that the lock pin 15 can engage in a retaining hole which will be described hereinafter.
Further, a discharging hole (unlock mechanism) 17 is formed in communication with the receiving hole 14 for discharging the back pressure acting on the lock pin 15.
On the other hand, the sprocket 2 which serves as the first rotor is provided with a retaining hole (lock mechanism) 18 at a position where the lock pin 15 can be received in the retaining hole 18 when the second rotor 6 assumes a most retard position relative to the first rotor assembly 1.
A pin releasing or unlocking hydraulic chamber 18a is defined between the inner wall of the retaining hole 18 and an outer wall of the lock pin 15 (FIGS. 22, 23).
The vane 6a having the receiving hole 14 formed therein is provided with a check valve (unlock mechanism) 19 for releasing the lock pin 15 from the state retained or locked in the retaining hole 18 by selecting either the valve timing advancing hydraulic chamber 9 or the valve timing retarding hydraulic chamber 10 in which higher pressure prevails, to thereby allow the pressure within the selected chamber to be fed into the retaining hole 18 in which the lock pin 15 is retained or locked (FIGS. 21, 22, 23).
The check valve 19 is hydraulically communicated to the interior of the retaining hole 18 by way of a first pin unlocking hydraulic pressure feed passage (unlock mechanism) 20 formed in the vane 6a of the second rotor 6 and a second pin unlocking hydraulic pressure feed passage (unlock mechanism) 21 formed in the sprocket 2 (FIG. 22).
Further, the check valve 19 and the valve timing advancing hydraulic chamber 9 are communicated with each other by way of a valve timing advancing hydraulic pressure distribution passage (unlock mechanism) 22. Similarly, the check valve 19 and the valve timing retarding hydraulic chamber 10 are communicated with each other by way of a valve timing retarding hydraulic pressure distribution passage (unlock mechanism) 23 (See FIG. 21).
Furthermore, the valve timing retarding hydraulic chamber 10 is communicated with a back pressure chamber 14a of the receiving hole 14 by way of a purge passage 24 (FIG. 21).
Now, description will turn to operation of the conventional valve timing control apparatus of the structure described above.
The ECU 1117 is so designed or programmed as to arithmetically determine or compute the target or desired phase angle on the basis of the operating state of the engine 1101. Further, the ECU 1117 arithmetically determines a detected phase angle indicative of the valve timing on the basis of the crank angle detected by the crank angle sensor 1115 and the cam angle detected by the cam angle sensor 1112, to thereby arithmetically determine deviation of the detected phase angle from the desired phase angle (i.e., difference or error between the desired phase angle and the detected phase angle).
Further, the ECU 1117 arithmetically determines or computes an energizing current value (conduction current value) or duty ratio for the oil control valve 1114 on the basis of the error between the detected phase angle and the desired phase angle so that the former coincides with the latter.
The oil control valve 1114 selects the oil passage for the cam phase actuator 1113 on the basis of the computed value to thereby control the valve timing by adjusting the hydraulic pressure feeding.
In the engine starting operation of the engine 1101, the oil control valve 1114 is so controlled that the hydraulic medium or oil is supplied or fed to the valve timing retarding hydraulic chambers 10 of the cam phase actuator 1113.
On the other hand, when the operation of the engine 1101 is stopped, there is the possibility that the oil within the cam phase actuator 1113 and the oil passage extending from the oil pump 1118 to the cam phase actuator 1113 may be discharged into an oil pan. In that case, when the engine operation is started, the air or the air containing oil within the oil passage is introduced into the valve timing retarding hydraulic chambers 10 to be discharged exteriorly from the cam phase actuator by way of the purge passage 24, the back pressure chamber 14a and the discharging hole 17.
Once the operation of the engine 1101 has been started, the hydraulic pressure is also introduced into the pin unlocking hydraulic chamber 18a from the valve timing retarding hydraulic pressure distribution passage 23. However, the lock pin 15 is held in the state retained within the retaining hole 18 under the influence of the urging means 16. In this manner, generation of abnormal noise due to rattling of the second rotor 6 with the lock pin 15 being released from the retaining hole 18 in the engine starting phase can positively be suppressed or prevented.
In the engine starting operation, in the course of the hydraulic pressure being fed to the valve timing retarding hydraulic chamber 10 from the oil pump 1118, the air trapped within the valve timing retarding hydraulic chamber 10 is exhausted from the apparatus via the purge passage 24 and the discharging hole 17. When the air has been discharged, the residual hydraulic pressure becomes effective due to the oil supplied to the back pressure chamber 14a to prevent the unlocking by increasing the hydraulic pressure at which the lock pin is released.
When the driver of the motor vehicle equipped with the engine system now under consideration depresses an accelerator pedal in succession to the starting of the engine operation to thereby issue a valve timing advancing command, the ECU 1117 responds thereto by controlling the oil control valve 1114 such that the hydraulic pressure is introduced into the valve timing advancing hydraulic chambers 9.
Then, the oil within the valve timing advancing hydraulic chamber 9 is introduced into the pin unlocking hydraulic chamber 18a by way of the valve timing advancing hydraulic pressure distribution passage 22, as a result of which the hydraulic pressure of the oil introduced into the pin unlocking hydraulic chamber 18a acts on the tip end of the lock pin 15 to push it in the releasing or unlocking direction against only the biasing force of the urging means 16.
Since the oil control valve 1114 is controllably set to the position where the oil is discharged from the valve timing retarding hydraulic chambers 10, the oil contained within the valve timing retarding hydraulic chambers 10 is discharged into the oil pan by way of the oil control valve 1114.
Consequently, the lock pin 15 is pushed outwardly from the retaining hole 18 to be released from the locked state. Now, the second rotor 6 is in the state to operate. More specifically, the second rotor 6 is rotated in the valve timing advancing direction under the hydraulic pressure within the valve timing advancing hydraulic chambers 9, whereby the valve timing advancing control is performed for the engine.
The conventional valve timing control apparatus for the internal combustion engine described above however suffers from a problem that when the desired phase angle changes rapidly from the position at which the lock pin 15 is retained in the retaining hole 18 due to rapid change of the engine operating state which occurs immediately after the operation of the engine 1101 has been started, lowering of the hydraulic pressure brought about by abnormal lowering of the rotation speed or for other reasons, operation of the second rotor 6 is activated early before the lock pin 15 has been disengaged from the retaining hole 18, as a result of which the lock pin 15 is twisted or sticked without being released from the retaining hole 18, making it impossible for the second rotor 6 to operate in the desired direction.
By way of example, in the case where the hydraulic medium or oil passages are so arranged that the lock pin 15 can be released from the locked state only under the hydraulic pressure for advancing the valve timing, when the second rotor 6 is activated rapidly in the valve timing advancing direction in response to the change of the operating state from the state in which the lock pin 15 has been retained in the retaining hole 18 at the most retard position, then the lock pin 15 can not be released from the state locked in the retaining hole 18 but twisted, making it impossible for the second rotor 6 to operate in the valve timing advancing direction, giving rise to a problem.
When the valve timing can not be controlled to the desired phase angle due to the twisting or sticking of the lock pin 15, degradation will naturally occur in respect to the drivability, fuel cost performance and the exhaust gas quality, presenting another problem.
In the light of the state of the art described above, it is an object of the present invention to provide a valve timing control apparatus for an internal combustion engine in which the problem of the valve timing advancing control failure due to entanglement or sticking (tangling in more general term) of the lock pin as mentioned above can successfully and satisfactorily be solved and thus the drivability, fuel cost performance and the exhaust gas quality of the engine can significantly be improved.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a valve timing control apparatus for an internal combustion engine, which apparatus includes a cam phase actuator composed of a first rotor capable of rotating in synchronism with a crank shaft, a second rotor fixedly mounted on a cam shaft for opening and closing an intake valve or alternatively an exhaust valve, and a lock mechanism for locking the second rotor to the first rotor at a first relative angle. And further includes an oil pump for generating a hydraulic pressure, an arithmetic unit for arithmetically determining a current value corresponding to a hydraulic pressure for releasing a locked state at the first relative angle to thereby shift the first relative angle to a second relative angle, and a hydraulic pressure regulating unit for supplying a hydraulic pressure for regulating a cam phase of the second rotor in dependence on the current value.
In the valve timing control apparatus, the arithmetic unit is so designed as to arithmetically determine a first current value for generating a first hydraulic pressure for releasing the locked state at the first relative angle and supply the first current value to the hydraulic pressure regulating unit for a predetermined time before shifting the first relative angle.
By virtue of the arrangements of the valve timing control apparatus described above, the valve timing can properly be controlled for the desired or target phase angle without being accompanied with tangling of the lock pin because the locked state can positively be cleared or released before the rotation of the rotor is started. Thus, drivability, fuel cost performance and exhaust gas quality of the internal combustion engine can be protected from degradation with much enhanced reliability.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.